memory access out of bounds – but why?

Question

I'm sharing a piece of memory between js and wasm, using 'imported' memory. in my assemblyscript code I'm not even accessing the preallocated memory and still get a RuntimeError: memory access out of bounds. I would like to understand why.

js:

const [width, height] = [100, 100];
const arraySize = width * height;
const pageSize = 64 * 1024;
const nPages = Math.ceil(arraySize / pageSize);
const memory = new WebAssembly.Memory({ 
  initial: nPages 
});
WebAssembly
  .instantiateStreaming(fetch('/build/optimized.wasm'), {
    env: {
      memory,
      abort: (_msg, _file, line, column) => {
        console.error(`Abort at ${line}:${column}`)
      },
    }
  })
  .then(({instance}) => {
    const bytes = new Uint8ClampedArray(memory.buffer);
    
    // A
    for (let i = 0; i < arraySize; i++) {
      bytes[i] = 1;
    }

    instance.exports.asdf(width, height);
  });

assemblyscript:

export function asdf(width: i32, height: i32): void {
  // B
  const arr = new Uint8Array(width * height);
}

when I remove either A or B it works.

---

edit:

weird: setting const [width, height] = [39, 39]; also produces no error.

---

edit 2:

I'm using imported memory because all the examples I found do that. should I perhaps be creating arrays, etc. the way they show here? https://www.assemblyscript.org/loader.html#creating-arrays

Answer 1

I don't see any errors. See playground

Also this keep in mind when you allocate memory in AssemblyScript you may overwrite initialized memory before on the host side according your example.